In the related art, for example, when a flat plate-shaped welding target is welded, a stationary vacuum welding device configured to cover the entire welding target with a vacuum chamber and form a vacuum environment by vacuum-suctioning the vacuum chamber is known. However, when the welding target such as a compression container or the like is large, the vacuum chamber and the vacuum pump may be increased in size, and an enormous equipment cost and a wide installation space may be needed.
As a welding device corresponding to a large welding target, a movable vacuum welding device configured to move a vacuum chamber is known (for example, see Patent Literature 1). The welding device has a vacuum chamber that is relatively movable with respect to a welding target, and a seal section interposed between the vacuum chamber and the welding target, and maintains vacuum in the vacuum chamber as the seal section is adhered to the welding target.